Often a semiconductor technology's usefulness for the radio frequency (RF) space can be characterized by the transition frequency (fT)-breakdown voltage product known as the Johnson-limit. A high fT-breakdown product can be obtained by using semiconductor technologies that possess high electron velocity and wide energy band-gap. A gallium nitride (GaN) high electron mobility transistor (HEMT) is an example of a semiconductor device that possesses high electron velocity and a wide energy band-gap.
In addition, multi-transistor circuit topologies such as the Darlington-pair, cascode, and multi-stacked transistors can be used to improve the fT-breakdown product through higher voltage operation, fT multiplication, and thermal mitigation. These techniques are challenging as frequency and/or power is increased due to interconnect parasitics effects, especially in the millimeter wave (mmW) and terahertz (THz) regimes. Thus, it is desirable to have a transition frequency multiplier semiconductor device that has a structure with low inductive and capacitive parasitics. It is particularly desirable that the transition frequency multiplier semiconductor device be usable as a fundamental building block for extending the fT-breakdown product of short gate-length enhancement mode (E-mode) GaN transistor technology.